This invention relates to an improved process for the manufacture of hydrogen chloride (HCl) and an alkali metal sulfate from sulfuric acid and the corresponding alkali metal chloride. The process is applicable to various alkali metal chlorides including sodium, potassium and lithium chloride. The process comprises the continuous reaction between sulfuric acid and salt in a reaction chamber which provides for the counter current flow of gases and solids. These conditions are perfectly met in a direct fired rotary kiln.
Hydrogen chloride has been produced for many years from salt and sulfuric acid. Three centuries ago Johann Glauber discovered that when sulfuric acid is poured over common salt a colorless acrid gas is evolved. Later identified as hydrogen chloride, this gas is readily dissolved in water to form hydrochloric or muriatic acid.
The reaction first observed by Glauber was later employed by the French chemist Nicholas LeBlanc, who developed an industrial process for soda ash in 1794. In the front end of the LeBlanc process, sulfuric acid is reacted with salt to produce sodium sulfate which is subsequently converted with carbon and limestone to give sodium carbonate. Even though the LeBlanc Process was displaced by the Solvay process some seventy years later, hydrogen chloride continued to be produced by this chemistry.
The technology for producing hydrogen chloride changed very little over the years. An excellent summary of this technology was presented in a monograph published by the American Chemical Society in 1927. This publication titled, xe2x80x9cHydrochloric Acid and Sodium Sulfatexe2x80x9d by N. A. Laury provided details of the furnaces used to convert an intermediate in the process, namely, sodium hydrogen sulfate to sodium sulfate. Although of varied designs, these furnaces were without exception inefficient to operate. They produced a solid product that contained significant chloride impurities. Perhaps the best known furnace in this group was the Mannheim furnace, which was a muffle furnace with a cast iron pan and scrapers.
The first noteworthy departure in furnace design appeared with the proposed use of a fluidized bed reactor in 1955. Described in U.S. Pat. No. 2,706,145, the Cannon process for the xe2x80x9cProduction of Sulfates and HCl xe2x80x9d claimed to have overcome the drawbacks of the old technology. The fluidized bed process, however, had problems of its own. High conversions could not be obtained. And the well documented difficulties of fluidized beds plagued the process. Although the Cannon process received considerable attention, it has never been commercialized.
In later years there has been a lack of interest in the manufacture of hydrogen chloride from salt and sulfuric acid. The huge quantities of by-product hydrogen chloride produced in organic chlorinations shifted concern from HCl production to HCl disposal. More than enough by-product hydrogen chloride was being produced to satisfy the demand for this commodity chemical.
The present status of hydrogen chloride production would most likely continue unchanged except for the development of a relatively new organic reaction called oxychlorination. This process allows hydrogen chloride to be substituted for chlorine in certain organic chlorination processes. The most notable example is the production of ethylene dichloride from ethylene, hydrogen chloride, and oxygen.
Shifting technology again draws one""s attention to the manufacture of hydrogen chloride from salt and sulfuric acid. To succeed, however, any new process must meet the need for low capital investment, achieve high energy efficiency, and produce high purity products. It must also be easy to operate and require minimum maintenance.
It is therefore an object of the present invention to overcome the problems with the prior art.
Further, it is desired to provide for a process that can be extremely cost competitive.
Finally, it is an object of this invention to meet all environmental and safety concerns.
These and other objects, features and advantages of the invention will be apparent from the following description and the accompanying drawings.
The invention in one preferred embodiment concerns a process for the production of hydrogen chloride and alkali metal sulfate from sulfuric acid and the corresponding alkali metal chloride. The most common alkali metal chlorides used as feed materials are sodium, potassium, and lithium chloride.
The process comprises one reaction step which is operated on a continuous basis. The design of the reaction chamber provides for the counter current flow of gaseous and solid materials within this chamber. Back mixing of solids in the reactor is minimized so that a chloride-free sulfate can be obtained. Heat is applied to the reaction chamber to promote the chemical reactions which occur. The reactor is direct fired; the products of combustion from a burner become intimately mixed with the gaseous products within the reaction chamber.
In greater detail, reactants sulfuric acid and an alkali metal chloride in a molar ratio of approximately one to one are fed to the reaction chamber through a port at one extremity, and sodium sulfate product is withdrawn at an opposite location. When a rotary kiln is used as the reactor, the feed is introduced at the higher end of the kiln and sodium sulfate is withdrawn at the lower end. Gaseous products comprising hydrogen chloride and unreacted sulfuric acid are withdrawn from the chamber at a point near the inlet. The burner is located near the exit port for the sodium sulfate. Solids travel through the reaction chamber by means of gravity, a conveyor mechanism or some combination of both. The flow of gases depends on pressure differences.
The solid sodium sulfate is cooled after leaving the reactor and further processed as needed. The gaseous products are typically scrubbed to remove hydrogen chloride. Purified hydrogen chloride is recovered from the scrubbing solution. Unreacted sulfuric acid is recycled back to the reaction chamber.